1. Field of the Invention
The present invention relates generally to a method and apparatus (individual and collective protection filters) for removal of toxic gases. More particularly, the present invention is directed to an activated charcoal or carbon filter which is especially effective in removing cyanogen chloride from the air.
2. Description of the Prior Art
The use of activated carbon or charcoal which has been impregnated with metals and metal compounds as a filter to remove toxic gases has long been known. During both World Wars I and II, gas masks containing activated charcoal impregnated with copper and copper oxides were used to remove hydrogen cyanide. More recently, combinations of copper, silver and chromium have been employed with activated charcoal to remove such toxic agents as hydrogen cyanide and cyanogen chloride. The copper impregnated charcoal was called whetlerite, after C. Whetzel was instrumental in its development.
Military air filters have employed activated carbon impregnated with various compounds which are effective in removing specific toxic gases not readily controlled by carbon alone. In this country, a chromium catalyst, formed in situ on the carbon has been effectively used against the vapor cyanogen chloride. Use of this catalyst has, however, led to a number of problems.
1. The catalyst looses effectiveness when "aged" under certain conditions of humidity and temperature. PA1 2. Conditions required to form the catalyst including carbon type and processing methods are critical and may be hard to achieve. PA1 3. Chromium is carcinogenic and a potential hazard if carbon dust is inhaled.
Over the years a number of modified compositions have been tried which tend to improve the aging characteristic of the filter with respect to cyanogen chloride removal. These have been based on addition of organic amines to the chromium impregnated product. While a number of different types of amine compounds have been tested, the most effective has been triethylenediamine (TEDA). In the last 10 years the British Military has employed TEDA in combination with chromium salts to augment cyanogen chloride removal by their gas masks.
A search of the prior art has uncovered patents which disclose a variety of agents for enhancing the effectiveness of activated carbon for the selective sorption of gases.
U.S. Pat. No. 4,212,852 to Aibe et al. discloses a method for using activated carbon having supported thereon a metal compound of vanadium, molybdenum or tungsten to deodorize gases containing ammonia, amides and/or hydrogen sulfide.
U.S. Pat. No. 4,111,833 to Evans discloses activated charcoal impregnated with triethylenediamine and a mixture of iodine and potassium to remove iodine from a nuclear reactor effluent stream.
U.S. Pat. No. 4,040,802 to Deitz et al. discloses activated charcoal impregnated with a tertiary amine, such as triethylenediamine and iodine or bromine to remove methyl iodine from a nuclear reactor effluent stream.
U.S. Pat. No. 3,739,550 to Martin et al. discloses activated carbon impregnated with a mixed catalyst which includes a vanadium compound and at least one compound of potassium, lithium or barium to desulfurize carbon dioxide containing waste gases.
British patent No. 1,123,822 discloses activated charcoal impregnated with piperazine or triethylenediamine to remove iodine from nuclear waste effluent.
U.S. Pat. No. 3,355,317 to Keith et al. discloses the use of the oxides of cobalt, copper, zinc, iron and molybdenum on activated carbon to remove hydrogen cyanide from tobacco smoke.
U.S. Pat. Nos. 2,920,050 and 2,920,051, both to Blacet et al. describe the preparation of whetlerite type filters which include copper, chromium, silver and molybdenum impregnants.
In addition to the foregoing prior art patents, the comprehensive 1946 Government study entitled "Military Problems With Aerosols and Nonpersistent Gases", Volume I, sponsored by the Office of Scientific Research and Development (OSRD), describes the use of activated charcoal impregnated with various agents for removing noxious gases. Such uses are principally for gas masks devices.
Authored by Grabenstetter et al., Chapter 4 of the 1946 OSRD reports describing the use of copper, silver, chromium and molybdenum or vanadium impregnants on activated carbon to remove hydrogen cyanide and cyanogen chloride. Numerous organic base impregnations of charcoal are disclosed, including amines such as diethylene triamine and others.